Among the current crop of wonderful bass baritones, none is more sought-after than Thomas Quasthoff. But that's not all that makes him unique - he is also a thalidomide victim with wickedly outspoken views on art and disability.

WHATEVER else might ail the music industry, the market is booming in bass baritones. While lyric tenors are near-extinct and the latest hot soprano turns out on close inspection to be just another jumped-up mezzo, there have never been so many middle-low men, so many white-tied crooners who can melt a stony-faced audience with the opening phrase of Winterreise.

Consummate performer: 'I have absolutely no stage fright'

It's the flood that follows the famine. For half a century Dietrich Fischer-Dieskau withered any rival in vocal range with an austere glare and an iron grip on recording opportunities. If you wanted to buy a Winterreise, there were six discs in the shop of which five featured the King Fischer.

Even after he retired, Lieder were sung for years in a kind of tributary monochrome; it has taken a decade to reinject colour into the bass-baritone bloodstream.

A magnificent diversity now prevails. There is the nobly refined Thomas Hampson, the bearish yet delicate Bryn Terfel, the dark-hued Dmitri Hvorostovsky and the fast-risen Matthias Goerne, who some proclaim to be Fischer-Dieskau's rightful heir. And then there is Thomas Quasthoff, an altogether different pack of chords.

Quasthoff, who is in London for a pair of Bach concerts conducted by Andras Schiff, is a full-time professor of vocal studies who sings no more than 50 nights a year. "I have cut it back," he says, "because I don't want to be a guest at my own university, in Detmold, a stranger to my students."

His professorial authority is widely respected. Touring Germany with Beethoven's Ninth Symphony, he was stopped one day in rehearsal by Simon Rattle and asked to give extra coaching to the venerable Philharmonia Chorus. Quasthoff put them through a set of exercises to ease air pressure on the vocal tubes. "Wow!" exclaimed Rattle, hearing the improvement. "For me," says Quasthoff, "that was the most beautiful thing that could happen."

There is an infectious delight in everything he does, an invitation to colleagues and audiences alike to share his joie de vivre. At no time, eyes shut, is one aware of any constraint. Yet Quasthoff, 40, stands just four feet tall on legs that were stunted at birth, the consequence of a thalidomide pregnancy. He has almost no arms, his hands emerging just below the shoulders - "but the internal organs are fine", he grins. His mother, who was prescribed the sedative for insomnia, received less than £8,000 compensation from the pharmaceutical industry.

Tormented during infancy by surgical adjustments to his limbs, he was consigned by the education authorities to a school for cerebral palsy sufferers - until his parents resolved that he should experience normality. His father, a frustrated singer, took him at 10 years old to audition at the NDR radio station in Hanover. His talent was confirmed and a teacher was found.

Rejected by the music academy because he could not, for obvious reasons, play the piano, he continued to study privately and develop at his own pace. In 1988, aged 28, he won a national competition in Munich and was hailed by Fischer-Dieskau, no less, for his "wondrously beautiful voice".

Quasthoff hesitated, however, before making singing his vocation. He worked for the next six years as an NDR radio announcer, and then took up teaching.

"My parents said I should have a profession," he laughs. "They also insisted that I should train to be a banker, but I have forgotten those skills." For years, he sang jazz and cabaret in clubs for extra cash.

His celebrity is a recent thing, propelled by conductor demand. Claudio Abbado picked him for the O, Freunde! summons on his new Beethoven Ninth recording and Seiji Ozawa for Bach's St Matthew Passion. Deutsche Grammophon has awarded him an exclusive contract. Beset by operatic offers, he declined Daniel Barenboim's well-intentioned proposal to make his debut in Berlin as the hunchbacked Rigoletto.

Refusing to be typecast, Quasthoff finally agreed to play Don Fernando in Rattle's Fidelio in the 2003 Salzburg festival, followed a year later by Amfortas in Parsifal. "It was love from the first moment with Simon," he explains. "Every performance with him is like a musical party."

In the exuberance of success, his impediments are deemed irrelevant. "Why is it important that we should talk about disability?" he demands. "Can you imagine that I feel, as an artist, reduced by questions about my disability?

"I have a problem when people say I should be a hero for others who are disabled, because I don't live a disabled life. I have a beautiful, tall girlfriend and I live a normal life."

He lives alone in the town where he was born, his parents and elder brother nearby and his girlfriend, a vocal teacher, living 200 miles to the south with her two children; she often joins him on tour. When he needs a pianist for study or rehearsal, his 6ft 5in accompanist, Justus Zeyen, lives five minutes away.

Quasthoff's is an extraordinary tale of transcendence through art, a cruel fate overcome by a triumphant will. He may grumble that German critics compare him unfavourably with foreign singers, but he is satisfied that no concessions are made for his disability.

Unusually for a singer, he shows the same concern for diction as he does for pitch - a testament to years of poetry readings on NDR. His new album of Brahms and Liszt songs is exquisitely articulated, and he has been known to reject new repertoire because, in his view, the words do not match the beauty of the music.

His splendid voice spans the low C of a true bass and the middle C of most tenors. As a boy, he begged his teacher not to turn him into a tenor, feeling temperamentally more rooted in the nether regions.

H is contempt for those who blur qualitative distinctions and abuse the vocal art is positively withering.

"Andrea Bocelli is not an opera singer," he proclaims, "and I cannot understand why Pavarotti should have called him 'my successor'. What is that? Where are we living? Where is the quality? Why are big conductors making records with this guy? I am a teacher, and I know how hard it is to learn classical singing. He is not a classical artist."

To the suggestion that the blind Bocelli might have been formed artistically by the experience of adversity, Quasthoff retorts: "Obviously not formed well enough." To a DG proposal that he should record jazz and cabaret numbers, he replied: "I may do it some time, but if I do I don't want to sound like 'the classical' Thomas Quasthoff. I won't do that kind of Bocelli crossover."

He does not get involved in disability causes, but he has stood on German and Austrian concert stages and made political statements against the rise of the racialist Right. In the American South, he sings Paul Robeson encores. "I have absolutely no stage fright," says Quasthoff. "Perhaps because I don't just stand in front of an audience. I try to work with them, to take them with me on a journey. I don't think people are moved because I am disabled. I think it's because I have something to say."

Thomas Quasthoff is a soloist in 'St Matthew Passion' at the Festival Hall (020 7960 4242) on Sunday